1. Field
One or more embodiments relate to a cathode active material, a cathode including the cathode active material, a lithium battery including the cathode, and a method of preparing the cathode active material.
2. Description of the Related Technology
A lithium transition metal oxide is used as a cathode active material for a lithium battery, and examples of such a lithium transition metal oxide are LiNiO2, LiCoO2, LiMn2O4, LiFePO4, LiNixCo1-xO2 (0≦x≦1), and LiNi1-x-yCoxMnyO2 (0≦x≦0.5, 0≦y≦0.5).
A lithium cobalt oxide, for example, LiCoO2 is relatively expensive and has a limited electric capacity of about 140 mAh/g. When a charged voltage for LiCoO2 is increased to 4.2 V or more, 50% or more of lithium is removed and is present in the form of Li1-xCoO2 (x>0.5) in a battery. Li1-xCoO2 (x>0.5) is structurally unstable and its electric capacity is rapidly reduced over a charge and discharge cycle.
A compound that is formed by substituting some of cobalt atoms with other metals in the lithium cobalt oxide, for example, LiNixCo1-xO2 (x=1, 2) or LiNi1-x-yCoxMnyO2 (0≦x≦0.5, 0≦y≦0.5) has poor swelling suppression characteristics.
A lithium manganese oxide, for example, LiMn2O4, is relatively inexpensive and stable at room temperature. In general, a lithium manganese oxide is prepared through a solid state reaction method or a molten salt analysis method at high temperature. A lithium manganese oxide that is formed at high temperature has an unstable structure. Meanwhile, if a lithium manganese oxide is formed at low temperature, its primary particle diameter is reduced and thus its specific surface area is increased. Thus, cycle characteristics and stability of the lithium manganese oxide that is formed at low temperature may be lowered during high-temperature charge and discharge.